Evolution of composition of dairy manure supernatant in a controlled dung pit

Anaerobic conversion of dairy manure into biogas is an attractive way of managing this waste. It is well known that the hydrolysis of large molecules into small, directly biodegradable ones is the rate limiting step of the overall anaerobic process. The present work studies the development of the hydrolytic and acidogenic stages of dairy manure with different solid concentrations (40, 60 and 80 g VS/L) at ambient temperature (20 ° C). The purpose was to determine the operational conditions that provide a liquid fraction with a high soluble chemical oxygen demand (COD) and a high volatile fatty acids (VFA) content in manure before the methanogenic stage starts up. At 20 ° C, the evolution of the studied parameters showed that, in a controlled plug-flow dung pit, the hydrolytic and acidogenic stages progressed moderately in a continuous way during the 25 days that the experimentation lasted, whereas no methanization was observed. Supernatant COD and VFA concentrations increased 30% and 107%, respectively, for the 60 g VS/L samples. Manure was also operated at 35 ° C with a similar increase in supernatant COD but a higher increase in VFA, 154%. For both operational temperatures, the predominant VFAs were, in this order, acetic, propionic and butyric acids. During the operation at 35 ° C, the methanogenic stage started between days 20 and 25 for the samples with lower solids content, i.e. 40 and 60 g VS/L

Control of sulphide during anaerobic treatment of S-containing wastewaters by adding limited amounts of oxygen or nitrate

Sulphide generated during anaerobic treatment of S-containing wastewaters represents an environmental problem. Adding limited amounts of oxygen or nitrate (or nitrite) to biologically (or chemically) oxidise sulphide forms a simple process level strategy to control this problem. This short review evaluates the feasibility and limitations of this strategy on the basis of the results of bioreactor studies.Sulphide generated during anaerobic treatment of S-containing wastewaters represents an environmental problem. Adding limited amounts of oxygen or nitrate (or nitrite) to biologically (or chemically) oxidise sulphide forms a simple process level strategy to control this problem. This short review evaluates the feasibility and limitations of this strategy on the basis of the results of bioreactor studies.Spanish Ministry of Education and Science; AEA Technology Environment; Nova Energie; The Swedish Gas Centre; University of Southern Denmark

Biological decolorization of xanthene dyes by anaerobic granular biomass

Biodegradation of a xanthene dyes was investigated for the first time using anaerobic granular sludge. On a first screening, biomass was able to decolorize, at different extents, six azo dye solutions: acid orange 7, direct black 19, direct blue 71, mordant yellow 10, reactive red 2 and reactive red 120 and two xanthene dyes—Erythrosine B and Eosin Y. Biomass concentration, type of electron donor, induction of biomass with dye and mediation with activated carbon (AC) were variables studied for Erythrosine B (Ery) as model dye. Maximum color removal efficiency was achieved with 4.71 g VSS L−1, while the process rates were independent of the biomass concentration above 1.89 g VSS L−1. No considerable effects were observed when different substrates were used as electron donors (VFA, glucose or lactose). Addition of Ery in the incubation period of biomass led to a fivefold increase of the decolorization rate. The rate of Ery decolorization almost duplicated in the presence of commercial AC (0.1 g L−1 AC0). Using different modified AC samples (from the treatment of AC0), a threefold higher rate was obtained with the most basic one, \textAC\textH2ACH2, as compared with non-mediated reaction. Higher rates were obtained at pH 6.0. Chemical reduction using Na2S confirmed the recalcitrant nature of this dye. The results attest that decolorization of Ery is essentially due to enzymatic and adsorption phenomena.This work was supported by the PTDC/AMB/69335/2006 project grants (Fundacao para a Ciencia e Technologia, FCT, Portugal), BRAIN project (ID 6681, European Social Found and Romanian Government and the grant of the Romanian National Authority for Scientific Research, CNCS-UEFISCDI, project number PN-II-ID-PCE-2011-3-0559, Contract 265/2011